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Author: Subject: Flyback problem
Bromine
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[*] posted on 14-9-2007 at 07:34
Flyback problem


I have build flyback circuit (for ozone genration) from powerlabs and connetc it to flyback and doesn't work. I have flyback with built-in cascade and separate secondary from primary. I would like to ask someone who knows what circuit would work best with my flyback and why it does not work.



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12AX7
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[*] posted on 14-9-2007 at 08:32


Ok. Um, your schematic and layout?



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Bromine
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[*] posted on 14-9-2007 at 09:22


circuit

http://www.powerlabs.org/flybackdriver.htm#THE%20CIRCUIT%20

transistor gets hot, i dont now why i doesn't work.

picture

http://www.freespaces.com/brom213/br%20027.jpg

[Edited on 14-9-2007 by Bromine]

[Edited on 14-9-2007 by Bromine]




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chromium
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[*] posted on 14-9-2007 at 10:36


IIRC this circuit is kind of blocking oscillator. Months ago I did some experimenting with it but i used pnp transistor and reversed polarity.

I sometimes replaced reistors with potentiometers to find suitable values by trial and error.

It might be that your flyback transformer does not work. For testing this you can make yet another winding with say 10 turns and use it as secundary for powering some low voltage incadescent bulb. So you can see if oscillator is running.

[Edited on 14-9-2007 by chromium]

[Edited on 15-9-2007 by chromium]




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Xenoid
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[*] posted on 14-9-2007 at 10:57


I've built heaps of these, based on both the single and more common dual 2N3055 circuits. The most common mistake beginners make is to get the connections to the windings round the wrong way, so the transistor(s) and/or flyback are never switched properly! Try exchanging the start and finish of the primary and/or feedback winding in sequence. It it would appear your transistor is either permanently switched on or oscillating if it is getting warm. The flyback needs pulses of the right polarity to work properly.

Personally, I never understood why this design approach ever became so popular, although it is free running and works well (I believe it's based on the original Robert E. Iannini "Information Unlimited" design) it does involve ripping off the original coil and winding your own.

A better approach IMHO is to build a 555 timer circuit driving a power transistor or MOSFET. In this way you can drive any number of "high voltage" coils like flybacks, car spark coils, and 2-stroke magnetos. You can then adjust the 555 operating frequency and duty cycle to give different spark effects!

There are endless variations of 555 timer circuits on the web. Try "googling" (555 flyback circuit sparks "high voltage") or various combinations.

Regards, Xenoid
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Bromine
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[*] posted on 14-9-2007 at 11:58


how do I know when the coil is in right direction?



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[*] posted on 14-9-2007 at 12:07


First, try swapping the connections to the primary coil, if that makes no difference, then swap the feedback connections. If that doesn't work, you must have a more serious problem. It doesn't really matter which way you have wound your coils, just so long as you wire them into the rest of the circuit "the right way". Try every combination!

Regards, Xenoid
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franklyn
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[*] posted on 14-9-2007 at 12:22


What you have is known as an Armstrong oscillator, if it doesn't work it means it's
not oscillating duh. When you built this if you did not account for the phase polarity
of the coils then it is producing negative feedback instead of the positive feedback
that it requires for operation. Reverse the connections to the feedback coil.

You can test the flyback easily to see if it generates HV spark by jolting the primary
with a charged capacitor. Your transistor is heating of course because it is not mounted
on a heat sink. Anyway check to see that you have gain and it's not damaged.
Check the Emitter-Base circuit for forward bias it should be around 0.7 volt. Measure
Base-Collector voltage , if it is almost the power supply voltage then the transistor is
open , replace it.. If the Base-Collector voltage is very low then it is shorted, again
replace it.

Let us know of your success.

.
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Bromine
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[*] posted on 14-9-2007 at 12:40


I just tried with capcitor (2200uF 16V) and i did not se any sparks on secondary :S

[Edited on 14-9-2007 by Bromine]




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Xenoid
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[*] posted on 14-9-2007 at 13:54


Where did you get your flyback, out of an old TV, I assume!
Quite often, the first item to fail in old TVs is the flyback. Be careful i(f you ever get it going) when "drawing sparks". Put about a 10 Megohm resistor in series with the high voltage lead to limit current. A flyback transformer is not like an ordinary AC mains transformer, the pulses from the oscillator have to be the correct polarity! Have you tried reversing the primary winding connections?

Good luck, Xenoid
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[*] posted on 14-9-2007 at 23:38


this is a simple mistake to make, but did you check your E and B are the right way around: http://www.ese.upenn.edu/rca/instruments/Curvetracer/Image6....
there`s only a slight offset on these, and sometimes it`s easy mix them.

I use TIP3055`s in parallel and the 555 driver same as Xenoid, it works well, they`re easier to mount on a heatsink too :)




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[*] posted on 15-9-2007 at 00:44


probably flyback doesn't work, i have checked transistor, I change conections in coil and I still nothing happened.



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[*] posted on 15-9-2007 at 03:25


if you have a little AM radio tune to a dead station then place that by the ferrite, if it`s oscillating and it`s the secondary that`s borked, you`ll be able to hear it.



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[*] posted on 15-9-2007 at 08:22


that is Incorrect info Lambda!

2N3055`s can easily cover the several 10`s of KHz needed, I suggest you look up the tech spec of these!
in fact you can use them for LW, MW and low end SW radio transmitter outputs!

http://en.wikipedia.org/wiki/2N3055 may interest you.

[Edited on 15-9-2007 by YT2095]




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[*] posted on 15-9-2007 at 08:42


Sorry @YT2095, I had edited my post after your reply !

2N3055 Transistors are not designed for high Power fast switching purposes, they are far to slow, and therefore dissipate far to much waste power. I have never understood why they are so popular in these kind of designs, maybe because they are so cheap, and are then used in a cheap shitty design approach. Transistors used in VGA Monitors are fast switchers, with very steep turn-on and turn-off times, together with a design that indeed makes use of this fast on-off momentum where only minimum power is lost. It is irrelevant how much power a transistor can handle, lost power is lost power, and you somehow have to get rid of it before overcooking the stew. A good design with transistors handling only a tenth of what the 2N3055 can handle may stay ice cold, and thus be a better choice and far better design.

Richie's Tesla Coil Web Page
http://www.richieburnett.co.uk/tesla.shtml

DRIVER CIRCUIT THEORY - Page 1
http://www.richieburnett.co.uk/sstate2.html

DRIVER CIRCUIT BEHAVIOUR - Page 2
http://www.richieburnett.co.uk/sstate3.html

Here he explains beautifully how to approach this problem, so please read his excellent website. Then it will become clear what I mean and which complex variables are involved. Dump this 2N3055 nonsense, and use a few old VGA monitor HV transistors after you have read Richie's Tesla Coil Web Page. A 555 also suffers from slow turn-on and turn-off problems, and this may be compensated in a good design approach by using a Totem Pole Driver Stage. But here again, first read Richie's Tesla Coil Web Page.

Regards,

Lambda.

[Edited on 15-9-2007 by Lambda]
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[*] posted on 15-9-2007 at 09:19


http://en.wikipedia.org/wiki/2N3055

Quote from wikipedia.org:

Another use is to drive the primary coils of TV line output transformers, to allow low cost high voltage generators to be built.

Reply:

This dose not mean that it is the best choice, or best design strategy and approach. It just means that it is used again and again in a cheap, cheap, cheap, lowsey design that can be improved a lot with much and much higher efficiency. 2N3055 do not have steep switching specs..., and much more can be said about this than only steep switching specs, for this is only one aspect of the complex interaction which can bring down efficiency dramatically and overheat the transistors and coils. Driving a Rolls Royce is no guaranty for a smooth ride, if the roads are left unpatched with deep holes. Then even a Rolls will brake down eventually prematurely. It's the combination of a good Car and good Road that makes up for a good ride. A Lada on a good road may then become Heaven in Hell for this reason, and a 2N3055 ain't no Rolls Royce in Tesla Driving Stages, ... But I get your point, and hope that you also see what I am Moaning and Groaning about, ... History repeats itself, so do we ever learn from the past ?

Regards,

Lambda.

[Edited on 15-9-2007 by Lambda]
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[*] posted on 15-9-2007 at 09:38


well if it switches to 2.5 MHz, then 20 or 40 or even 80 KHz is no big deal for it, granted the slew rate isn`t fantastic but they`re perfectly acceptable for Audio devices and a little above at high power and will indeed blast out several 10`s of watts in RF power too (ideal for sine waves slow slew).



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[*] posted on 15-9-2007 at 09:58


The 2N3055 can be used successfully in a TV Flyback Design, but I personally have reservations in regard to a direct coil feedback design as seen in most ones. A lot can be improved on this minimalistic approach. So, ... let's take the ride with a 2N3055 and Beef-Up a nice Design which will make @Bromine's day ....

Regards,

Lambda.

[Edited on 15-9-2007 by Lambda]
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[*] posted on 15-9-2007 at 10:12


in this instance I agree, It`s a reactive circuit and the 2n`s base gain isn`t great without a driver, a Push Pull or a set it up as a Hartley oscillator would be better.
typically a BU trans would be used, but the 2n or TIP 3055 is good for this app.




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[*] posted on 15-9-2007 at 10:22


A +100V supply and a suitable MOSFET driven by a squarewave oscillator (a 555 is sufficient, having edge time around 200ns) works quite nicely. Before removing the FBT, trace the HOT (Horizontal Output Transistor) to the primary winding on the FBT. The primary is usually the first two (or last?) pins on the FBT base. A +100V supply is typical, and may even be marked on the silkscreen.



This was a ~45% duty cycle square wave driving a 800V, 4A MOSFET (removed from the same monitor's power supply). You can see a faint arc at the bottom of the picture. The power supply was +50V, so less than 1/4 power output. In flyback mode, power output depends jointly on supply voltage, clock frequency, and duty cycle (until current becomes continuous, where the relation changes some).

Tim




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[*] posted on 15-9-2007 at 10:34


yup and a trip 5 under a small heat sink (the silver one by the pots):



here`s the other 2:



you can Just about see the TIP30555 onder the black heat sink here:



sorry about the not so great pics, but it gives an Idea at least.


[Edited on 15-9-2007 by YT2095]




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